The present invention relates to guide wires for the insertion of catheters into the human or animal body and in particular, though not exclusively, to guide wires suitable for the insertion of the catheter into the bladder.
Insertion of a flexible catheter into the human bladder via the supra-pubic region can present particular problems. In one conventional technique, a large bore needle having an internal diameter capable of receiving the flexible catheter is used to penetrate the skin, underlying tissue and bladder. A flexible catheter is then introduced into the needle and inserted into the bladder, following which the needle may be withdrawn. This requires the use of a needle having large diameter sufficient to accommodate a catheter and of sufficient strength to penetrate the relative tough supra-pubic tissue area. This requires the use of a needle having an outside diameter that is significantly larger than the outside diameter of the flexible catheter (which itself is typically approximately 4 or 5 mm), thereby forming a hole in the tissue significantly larger than strictly necessary. Great care has to be exercised by the clinician introducing the needle to avoid over- or under-penetration of the needle.
In another conventional technique, a trocar having a stiff penetrative tip (e.g. of medical grade stainless steel) and a stiff outer plastic sheath is inserted into the bladder through the supra-pubic region. The trocar is then withdrawn through the sheath, leaving the sheath in situ, penetrating the bladder through the supra-pubic region. A flexible catheter is then introduced into the bladder through the sheath. The plastic sheath is of the peelable variety, so that once the flexible catheter is introduced into the bladder, the sheath can be split along its entire length, stripped away from the flexible catheter and removed from the body. This leaves the flexible catheter in situ. A potential drawback with this technique is that the initial penetration of the supra-pubic region is, like the previously described technique, performed with a penetrative instrument having an outside diameter of similar dimensions to the flexible catheter that is eventually introduced (e.g. of the order of 5 mm or so). Therefore, again, the clinician must exercise great care to avoid over-penetration of the bladder and potential damage to the opposite bladder wall.